Unraveling molecular trends in the oxidative H abstraction on the positive electrode of Li-ion batteries

The (electro-)chemical reactivity between organic solvents and electrode surfaces is one of the main issues limiting the cycle life of Li-ion batteries [1]. At the positive electrode, composed of transition metal oxides, interfacial reactions contribute to capacity fading, which depends on the oxide chemistry [2]. For instance, substituiting Co and Mn with Ni, forming Ni-rich NMC electrodes, can increase the energy density of the battery, but reduces capacity retention and cycle life. The presence of Ni in a high oxidation state can initiate C-H activation of solvent molecules, as also reported by experimental evidence [3,4,5]. In this study, we have investigated the oxidative degradation of carbonate solvents and other classes of organic molecules via C-H activation on late transition metal oxide positive electrodes in Li-ion batteries by using density functional theory calculations [6]. We demonstrated how C-H activation changes from deprotonation to oxidative hydrogen abstraction, as the lattice oxygen activity increases, by moving the Fermi level closer to the oxygen 2p-band center. By analyzing a set of small molecules, spanning a broad range of functional groups and substitutions, we show how relevant energies of the isolated molecules impact the driving force for degradation reactions at the surface of LiNiO2, an oxide with high lattice oxygen activity. We found that C-H bond oxidation free energy, measured as the free energy to substitute a C-H with a C-OH bond for the isolated molecule, is the descriptor with the most predictive power for the C-H activation driving force on an oxide with highly reactive lattice oxygens. Leveraging this descriptor, we identified promising S-and F-containing compounds with enhanced stability toward C-H activation. These findings pave the way for a rational design of novel electrolytes that minimize degradation and impedance growth of Ni-rich LiNixMnyCo1-x-yO2 (NMC) electrodes. [1] J.-M. Tarascon, and M. Armand, Nature 2001. [2] D. Aurbach, B. Markovsky, A. Rodkin, E. Levi, Y.S. Cohen, H.-J. Kim, and M. Schmidt, Electrochimica Acta 2002. [3] L. Giordano, P. Karayaylali, Y. Yu, Y. Katayama, F. Maglia, S. Lux, and Y. Shao-Horn, The Journal of Physical Chemistry Letters 2017. [4] Y. Yu, P. Karayaylali, Y. Katayama, L. Giordano, M. Gauthier, F. Maglia, R. Jung, I. Lund, and Y. Shao-Horn, The Journal of Physical Chemistry C 2018. [5] Y. Zhang, Y. Katayama, R. Tatara, L. Giordano, Y. Yu, D. Fraggedakis, J.G. Sun, F. Maglia, R. Jung, M.Z. Bazant, and Y. Shao-Horn, Energy & Environmental Science 2020. [6] L. Giordano, Y. Yu, K. Akkiraju, N. Ceribelli, J.A. Johnson, Y. Shao-Horn, in preparation 2025.